Element set for air preheaters



Dec. 14, 1954 G. K. w. BOESTAD ETAL 2,696,975

ELEMENT SET FOR AIR PREHEATERS Filed May 17, 1950 a 3 Sheets-Sheet 1 AINV'ENTORK s 7 AV 1 5 ifii' ATroRNl-zv 14, 1954 e. K. w. BOESTAD ETAL2,595,976

ELEMENT SET FOR AIR PREHEATERS F iled May 17, 1950 I 3 Sheets-Sheet 2T211215 Tll:'.5. ."i

Dec. 14, 1954 G. K. w. BOESTAD ETAL 2,696,976

ELEMENT SET FOR AIR PREHEATERS Filed May 17, 1950 3 Sheets-Sheet 3 l I II A ATTORNEY 2,696,976' ELEMENT SET FOR AIR PREHEATERS Gustav K. W.Boestad, Lidingo, and --Knrt S'v'en'ningson, Johanneshof, Sweden,assignors, by mesne assignments,

to Jarvis C. Marble, New York, N. Y., Leslie Merrill, Westfield, N. 1.,and Prcy H. Batten, Racine, Wis., trustees Application May 17, 1950;Serial'No. 162,524 Claims priority, application Sweden Jnne 22, 1949 13Claims. (c1; 257-6) The present invention relates to element platesforheat exchangers of the regenerative type in which, as is known,

the heat emitting and heat absorbing media alternately flow through thechannels between the suitably arranged plates in an element set whichthereby is alternately heated and cooled. The rotatingLjungstrem-preheatei may be mentioned as a typical example of a"heatexchanger of the regenerative type.

In order to obtain the best possible result from lth 'ei.

viewpoint of heat economy, the heat transfer between gas and elementplate should be as high as possiblewhileatthe same time maintaining aminimumpressured'ro'p'of.

thegases through the channel and'also maintaining the cost of the platestructure and its assembly. at aminimumu The possibility of blowing theplate surfaces free from soot and the like by means of air-or steam jets.isalso of importance for the desig'n'of the channels between the platesand thusfor the design of the'plates' themselves.

Furthermore, said plates should also be of such construc-;

tion that they are soiled as little as possible by flue gas particles.

A conventionalembodiment'of element plates is'. dis closed in U. S.Patent No'. 2,023,965. According to that patent the plates in theelementset are' 'made alternately as corrugated and ridged plates.Between each pairof plates channels are formed which ar'e completelyseparated from the other channels'which are formed between the sameadjacent pair of plates.

The corrugations or undulations in the plates have for their object thedeflection of the main gas current so that in each channel, definedbetween two distance ridges, there are formed laterally directedsecondary eddies whereby the heat exchange is improved. However, thisimprovement of the heat exchange evidently is due not only to thecreation of secondary eddies but also due to the fact that the boundarylayer formed along each plate surface at the passage of the gas isagitated. The more effectively this boundary layer is interrupted oragitated in some other way and the more often the gaseous mediumimpinges the plate surfaces, the more effective becomes the heatexchange. Therefore, the invention has for its object a novel plateconstruction for element sets for heat exchangers of the kind mentioned,through which this purpose is satisfied to a very great extent.

For this purpose, the element set according to the invention issubstantially characterized in that it contains plates which areprovided with slits and which are deformed between the slits in such amanner that each plate surface becomes composed of a number of surfaceportions partially separated from each other by means of slits or spacesand deviating from the base plane of the plate.

In order to reduce the heat conduction in the plate material itself fromhot to colder portions, it has previously been suggested to provide theplate with a number of narrow apertures or spaces formed by means ofpunching operations carried on the plate material. This way ofproceeding is only of importance if the plate thickness is great inrelation to the channel length, because the efficiency of the heatexchanger without said apertures would be reduced due to the heat flowin the plate proper.

Thus, the invention is substantially characterized in that the elementplates consist of surface portions displaced in different directionsrelative to each other and tit partially separated from each other byspaces. By this means, favourable conditions arepreated for the; heattransmission as the bondary layeralongthe plate surfaces isbrokenudownand destroyed before/ it reaches the nextplate' strip and the eddiesvthus formech in combination with the repeated impingement against thefollowing:

plate edges, acts to increase the heat transmission to a higher extentthan that corresponding to the increase in pressure drop.

The invention will be described hereinaftenmore in.

detail with-reference to the accompanying. dr'awings in which somesuitable embodiments are shown by way: of m l In the drawings Fig. 1 isan elevationof a structure embodying the invention;

v Figs- 2 and 3 are sectionstaken on lines 2"2 and"3 -3 of 1respectively; I I T Fig. 4 is a modified form of the structure shown inFig. 1; Y

Fig, Sis aview similar to Fig. 1 of another structure embodying theinvention; v

Figs. 6-7 are sections indicated on the lines 66 and 7'7 respectively ofFig.5; v

Fig. 8 is a view similar to Fig. 1,,of'still another form of structureembodying the invention;

Figs. 8a and 9 are sections taken on thelines 8 a-8a and 9 9respectively of Fig. 8';

Fig...l0 is a. section of amodification of the structure shownin Fig;8'; t v.

Fig., 1 1 is a" view similar. to Fig. lshowingstill another form ofstructure embodying the invention; p

lla'is a section taken on the line 11a11a of Fig. 12 is a View similarto Fig.1 showing still another structure embodying the invention;

. F'g. 12a is a section taken on the line 12tl-12t1 of Fig; .13; v

Fig; 13 is a'sec'tion on the line 13-13 of Fig. 12;. Fig'.. 141is asection showing a modified form of the structure illustrated in Fig. 12;

Fig. 15 is a view similar to Fig. 1;

Figs. 15a; and.16 are sections taken on lines 15a15a ahd."16 16respectively of Fig. 15;

Fig. 17'isa'v1ew similar to Fig. 1 showing still another structureembodying the invention; and

Fig. 18 is a section taken on the line 18-18 of Fig. 17.

In Figs. 1 to 3, the reference numeral 10 designates an element plateprovided with pressed-up straight ridges 12 which serve as distanceelements between the different plates and at the same time createstraight flow passages 14 for the gas. Between the ridges 12 the platesare cut as indicated at 16, and the surface portions 18 thus obtainedare pressed out to oblique position as is clearly seen from Figs. 2 and3. In usual cases the pressing should be carried out so that not morethan at least one-half of the channel width, that is, the distancebetween two element plates is free from the oblique surface portions 18.g The ridges 12 are of the usual design but they may also be designed inanother manner. The smooth plate 20 shown in Fig. 3 constitutes part ofthe casing of a heat exchanger and encloses the element plates 10proper.

Fig. 4 shows plates 10 of the same design as that of Figs. 1 to 3, butin this case every second plate 10a is placed up and down with respectto the position of the pressed-out surface portions 18 and preferablyturned in such a manner that the surface portions between two adjacentplates form an angle to each other instead of running parallel in thesame direction.

The element plate shown in Figs. 5 to 7 is ridged and slit in the samemanner as in the previous embodiments, but the surface portions 18 aredisplaced in parallel relative to each other instead of obliquelypositioned, so that every second strip or surface portion 18 has beenpressed out or that all of them have been displaced alternatingly inopposite directions.

From the viewpoint of solidity and in order to further increase the heattransmission, it is advantageous to press the surface portions invaulted or bent form as shown in the two similar embodiments accordingto Figs. 8 and 9, or Fig. 10, or according to the two alternatives inFigs. 12, 13 and 14.

The surface portions need not necessarily be formed by means of slits 16situated at right angles to the ridges 12, but the slits may also bepositioned obliquely, as will be clearly seen from Fig. 11.

The ridges 12 may also be slit and deformed in the same manner as thesurface portions 18, the heat transition being improved because thewhole element plate is effectively utilized according to the principlesof the invention. Such an embodiment is shown by way of example in Figs.15 and 16.

According to another embodiment of the invention the surface portionsmay in connection with the cutting, or subsequently, be pressed out fromthe original plate surface to yoke shape and thereby at the same timeserve as distance ridges. An embodiment according to this principle isclear from Figs. 17 and 18. A plane plate without ridges is divided intogroups of slits 16 of suitable length, between which slits remainingparts 22 of the plate 10 serve to hold the surface portions 18 togetherwhich are bending back upon themselves in such a manner that the elementplate has the aspect shown in Fig. 18. The element plates shapedaccording to this embodiment may either rest directly on each other, orspecial plane or slightly corrugated plates 24 may be inserted betweenthe element plates according to Fig. 18, in which last-mentioned casethe pitch indicated need not be maintained.

We claim:

1. A pack of elements for heat exchangers comprising a plurality ofjuxtaposed plates providing between them a plurality of parallelchannels for flow of gaseous heat exchanging medium in paths of flowgenerally parallel with the plates, the plates forming at least one ofthe side walls of each of the channels being slit at a plurality ofspaced places along the length of the channel and at an angle to itslength and the portions of the plates between said slits being bent outof the planes of the plates to extend generally lengthwise of thechannels.

2. A structure as defined in claim 1 in which the slit plates includespaced parallel distance ridges engaging adjacent plates to formrelatively wide and shallow channels between the adjacent plates and theslits extend across substantially the entire distance between adjacentridges.

3. A structure as defined in claim 1 in which each of the opposite sidesof the respective channels is formed by a slit plate.

4. A structure as defined in claim 2 in which the bent out portions areinclined at an acute angle with respect to the planes of the plates.

5. A structure as defined in claim 4 in which the bent out portions arein the form of shallow arches considered in the direction of gas flowthrough the channels.

6. A structure as defined in claim 4 in which the bent out portions aresinuous considered in the direction of gas flow through the channels.

7. A structure as defined in claim 2 in which the major parts of thebent out portions are parallel to the planes of the plates and offsettherefrom by a distance less than the height of said ridges.

8. A structure as defined in claim 7 in which alternate bent outportions along the length of an individual plate extend from oppositesides of the plane of the plate of which they form a part.

9. A structure as defined in claim 8 in which the distance ridges arealso slit at a plurality of spaced places along the length of thechannels, the portions of the distance ridges between the slits beingbent out alternately from opposite sides of the plate.

10. A structure as defined in claim 2 on which the slits are obliquewith respect to the lengths of the channels.

11. A structure as defined in claim 1 in which the bent out portions areyoke shaped to provide rows of distance elements for engaging andspacing adjacent plates.

12. A structure as defined in claim 11 in which alternate bent outportions of individual rows project from opposite sides of the plane ofthe plate.

13. A structure as defined in claim 12 in which the pack 'comprisesalternating slit and imperforate plates.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,762,446 Ljungstrom June 10, 1930 2,023,965 Lysholm Dec. 10,1935 2,227,836 Linderoth Jan. 7, 1941 FOREIGN PATENTS Number CountryDate 67,903 Norway June 5, 1944 512,265 Great Britain Aug. 31, 1939

